Eyes of human beings move for various reasons. There are voluntary movements and involuntary movements. The tracking of the eye movements has various applications such as detecting drowsiness of drivers.
Eye tracking devices are often divided into contacting and contactless devices. There are devices that look into the eye using a camera system and deduce eye movements from optical signals. There are also devices in which a sensor is attached to the eye like a contact lens, or in which electric changes about the eye are measured with pads connected to the skin around the eye.